Thanks, Tim
In fact I did select and paste the [[NAME]] etc with some of the surrounding text from the Retirees' certificate into the Finishers' certificate - with some trepidation in case I messed the whole thing up and had to redo the whole event - and it worked. The certificates print out properly. I have Georgia font rather than Times, but I can live with that if I have to.

I might try changing the font as as you suggest, but I'll do that with an experimental event first - once bitten, twice shy ...

I think if you've edited the merge fields your only option is to start again with a new event.

I've tried copying & pasting and also tried editing the HTML but it doesn't pick up the new/pasted fields as merge fields, even though there is no apparent difference in the HTML.

It's easy enough to change the font of the merge fields when they are working - just highlight the field you want to change & then set the font from the drop-downs.

Pacer manual page 70 states
"The text in the double square brackets is variable ? again it is clear what these mean. You can move them around to different points in the certificate but DON?T delete them or edit the text within the square brackets"

I did, found I was getting [[ NAME]] and [[ROUTE]] instead of ?Joe Bloggs? and ?30 miles? then read the manual 

How do I get it back doing what it should, and how do I change the [[NAME]] etc text to Times New Roman rather than Georgia?

Can I just select and paste from the retirees certificate below and change the wording? This doesn?t solve the font problem though.